The present invention relates to a novel tank construction for carrying a cryogenic fluid such as liquefied natural gas at about ambient pressure, and more particularly, to a double wall cargo tank of this type.
In the transportation of cryogenic fluids such as liquefied natural gas, various tank configurations have been designed including free-standing flat and corrugated plate tanks, and single and double wall tanks. These tanks are typically supported either above or upon a bed of thermal insulation within the hull of the transport ship.
The flat plate design requires either that the insulation space between the tank walls and the ship structure be completely filled with load bearing insulation or alternately that a plurality of stiffening members be welded to the tank walls so that adequate strength is provided. These stiffeners conventionally lie inside the primary barrier of the tank, pass through openings formed in the internal structural support webs of the tank, and are welded to the primary barrier and to the internal structural support webs. Tank construction of this nature is very difficult and manual welding is required which increases the cost and the time of construction of the tank. Accordingly, it would be desirable to provide a means of stiffening the tank walls which would avoid the tedious and costly manual welding typically associated with conventionanl stiffeners.
Accordingly, it is a broad object of the present invention to provide a new and improved double wall tank design in which the stiffeners are arranged so as to enable automatic welding techniques to be employed.
It is a further object of the present invention to provide a double wall tank design in which the secondary barrier is supported by the stiffeners.
It is another object of the present invention to provide a double wall tank design in which the stiffeners form a part of the liquid and gas-impervious secondary barrier.
It is still another object of the present invention to provide a double wall tank design in which means are provided for transferring part of the load normally carried by the sides of the tank to the tank's centerline longitudinal bulkhead.
It is yet another object of the present invention to provide a double wall tank design in which the weight of the primary structural support web system is reduced.
Still another object of the present invention is to provide a double wall tank design in which the insulation means acts as a support for the liquid and gas-impervious secondary barrier.
Still a further object of the present invention is to provide a double wall tank design in which the insulation means located outside the secondary barrier is formed by a plurality of insulating panels which are easily assembled and disassembled.
These and other objects of the present invention, as well as many of the attendant advantages thereof, will become more readily apparent when reference is made to the following description taken in conjunction with the accompanying drawings